Process for bonding a hot melt polymeric coating to a substrate



United States Patent 3,470,015 PROCESS FOR BONDING A HOT MELT POLY- MERIC COATING TO A SUBSTRATE Jesse P. Shanok, Brooklyn, and Victor Shanok, New York,

N .Y., assignors to Glass Laboratories Company, Brooklyn, N.Y., a partnership No Drawing. Continuation-impart of application Ser. No. 500,184, Oct. 21, 1965. This application Apr. 8, 1966, Ser. No. 541,092

Int. Cl. B4411 1/092 US. Cl. 117-72 5 Claims ABSTRACT OF THE DISCLOSURE Process of hot melt coating. The hot melt is applied to a base wet with a liquid anaerobic curing composition. The application of the hot melt covers the liquid anaerobic curing composition, heats it and excludes air from it, thereby promoting its polymerization.

This application is a continuation-in-part of our application Ser. No. 500,184 filed Oct. 21, 1965.

This invention relates to the bonding of a polymeric material to a base, and relates more particularly to the application of a layer of polymeric material to a metal foil base.

One aspect of this invention relates to the discovery that in a hot-melt coating process, the adhesion of a polymeric material such as cellulose acetate butyrate to a base such as aluminum foil can be increased by providing the base with a very thin coating of a liquid which thoroughly wets the foil and which is in turn wet by the molten polymeric material.

In one highly convenient embodiment of the invention the liquid is deposited onto the base in thicker layers than is needed, then part of this layer is evaporated off until only a very thin layer of the liquid remains, and then the base carrying the very thin layer is brought into contact with the molten polymer. It is found that if the evaporation is continued until all the liquid is driven oil from the base before molten polymer is applied, the adhesion is poor. If, on the other hand, the molten material is applied before evaporation has proceeded sufficiently to reduce the thickness of the layer to the desired extent, a less desirable product is obtained in that the polymer is bubbly.

The liquid can be applied in substantially undiluted condition to the base and then partially evaporated. Alternatively, a mixture of the liquid and a more volatile diluent can be applied followed by evaporation of the diluent.

The process is particularly useful in continuous steadystate coating operations, in which a web of the base material is continuously forwarded to a hot-melt coating zone. Here the moving web approaching the coating zone can first pass through a zone where a layer of the liquid is applied and then through an evaporative zone in which a substantial part of that layer is removed. No measurement of the thickness of the applied liquid layer or of the amount of evaporation is needed. It is suflicient for the operator merely to pre-set the conditions in the evaporative zone (e.g. by regulating the temperatures of any heaters used in that zone or by altering the distance between such heaters and the moving web) after simple preliminary tests. Thus, in these preliminary tests, it the product leaving the hot-melt coating zone has a bubbly polymeric layer the amount of evaporation should be increased, while if the adhesion is not high (indicating substantially complete removal of the liquid layer before it comes in contact with the melt) the amount of evaporation should be decreased. After making these simple tests ice and the appropriate corrections in the conditions in the evaporative zone, the operator can permit the apparatus to run continuously, under substantially steady state conditions, without further adjustments. It has been found that the thickness of the liquid layer on the base entering the hot melt is not narrowly critical; that is, after just sufiicient liquid has been removed to eliminate bubbling, there is still enough liquid on the base to provide a reasonable Working range before the improved adhesion is lost by carrying the evaporation too far. The practical working range is wider when the wetting liquid is not highly volatile.

In one preferred embodiment, the liquid applied to the base is a low viscosity polar organic liquid having a low molecular weight, e.g. a molecular weight below about 500, advantageously below about 200. The material may, for example, be an ester, alcohol, or ketone, e.g. ethylene diacetate, B-chloroethanol, ethylene dichloride (an ester of glycol and hydrochloric acid), vinyl acetate, vinyl butyrate, chloroacetone or ethyl acrylate. The liquid is advantageously one which is a solvent or swelling agent for the polymeric material to be applied to the base. While polymerizable monomers may be employed the conditions, in this embodiment of the invention, are advantageously such that no substantial polymerization or other chemical reaction of the monomer occurs prior to the contact of the base with the hot melt. Preferably, the liquid employed is colorless and stable to heat, at the temperature of the hot melt, and stable and non-discoloring under ultraviolet light. It should wet the base material readily. The thickness of the layer of liquid on the base is advantageously below about inch (e.g. .0001 inch) but this layer may be substantially monomolecular or only a few molecules thick.

It is found that ordinary aluminum foil, such as annealed rolled foil, may be used in the process of this invention without the need for any preliminary degreasing or other processing.

According to one aspect of this invention, there is applied to the aluminum foil base a polymerizable liquid whose polymerization is inhibited by contact with air (an anaerobic curing composition stable in air) the polym erization being promoted when the hot melt covers the polymerizable liquid, heats it and substantially excludes air from it. In this case, the hot melt may be applied to the monomer-treated base under conditions of decreased oxygen pressure, e.g. in a nitrogen atmosphere or under vacuum. The hot melt may, if desired, be deposited onto the liquid-treated 'base as a supported flowing sheet or tube of molten material; thus, the molten material may be passed through a Zone in which it is confined in sheet or tube form and the monomer-treated base may be brought into contact with the molten material in that zone.

The following examples are given to illustrate this invention further.

Example 1 A strip of annealed rolled aluminum foil (carrying, as is conventional, sufiicient rolling lubricant to permit it to unwind freely from the roll on which it was mounted) was unwound continuously and passed directly, while maintaining the foil in its flat condition and without changing its direction, successively through a liquid-applying station, a heating zone, a bath of molten cellulose acetate butyrate free of volatile solvent (Tenite Butyrate, M flow) and a sizing die, at the rate of feet per minute and then cooled to room temperature. At the liquid-applying station, a film of ethylene diacetate about 0.001 inch in thickness was applied to both sides of the moving foil at room temperature. In the heating zone the strip of foil was passed between electric radiant heaters which evaporated off the major part of the applied liquid. The bath of molten 3 cellulose acetate butyrate was maintained at a temperature of 350 F.; the strip took about /2 second to travel through the bath. The sizing die was such as to leave a layer of the cellulose acetate butyrate 0.02 inch thick on each side of the strip, the latter being completely embedded in the clear cellulose acetate butyrate. The resulting product had a metallic appearance, the shiny surface of the aluminum being visible through the clear plastic. The product could be bent 180 on itself without developing crinkles in the embedded aluminum foil, showing that the aluminum adhered to the plastic material.

Example 2 Example 1 was repeated, substituting chloroethanol for the ethylene diacetate, with similar results.

Example 3 Example 1 is repeated except that there is employed, as the liquid, an anaerobic curing composition which is stable against polymerization when exposed to the air but which polymerizes at room temperature when air is excluded. The composition contains an acrylic polyester of a polyhydric alcohol (e.g. tetraethylene glycol dimethacrylate or diglycerol tetraacrylate), a latent initiator of polymerization such as a non-polymerizing hydroperoxide (e.g. cumene hydroperoxide or p-menthane hydroperoxide), preferably together with an accelerator (such as a tertiary amine, e.g. triethylamine, ascorbic acid, an organic phosphite, or a quaternary ammonium salt) and an inhibitor such as a quinone (e.g. 1,4-benzoquinone or 2,5- dihydroxybenzoquinone). A typical formulation, which is stable for many months (e.g. 1 yr.) in air at 25 C., contains tetraethylene glycol dimethacrylate mixed with 7% cumene hydroperoxide, 2% triethylamine, and 200 p.p.m. of 1,4 benzoquinone. No intermediate heating zone is used.

While this invention has been illustrated using an aluminum foil base, with which it has found its greatest utility, it may be employed with other base materials. Particularly suitable are other metallic bases, especially foils, e.g. tin, stainless steel, copper, brass, or zinc, or other smooth-surfaced bases such as glass. The use of other polymeric materials besides cellulose acetate butyrate for hot melt coating is also within the broader scope of this invention; thus there may be employed such other cellulose esters as cellulose acetate or cellulose propionate; polyvinyl resins such as polyvinyl acetate, polyethyl acrylate, polystyrene, polyethylene or polypropylene; or other high polymers, for example, condensation polymers such as polycaprolactam or other nylons (e.g. nylon 66) or polyesters such as polyethylene terephthalate.

The liquid may be applied in any convenient manner. Thus, it may be padded onto the base, as by passing the base between pads wet with the liquid, or it may be applied by metering rolls (e.g. knurled rolls dipping into baths of the liquid), or it may be doctored onto the base in known manner, etc. The partial removal of the liquid may be promoted by subjecting the base carrying the liquid film to subatmospheric pressure (as in a vacuum chamber) to increase the evaporation of the liquid. In a preferred form the liquid is applied over the whole surface of the foil base, but it may be applied only to limited areas, e.g. in a pattern of spaced dots or narrow parallel lines extending longitudinally of the foil strip.

What is claimed is:

1. Process of coating a base material with a hot melt coating of a polymer, which comprises applying to the base material, prior to the application of the hot melt thereto, a thin layer of a liquid which wets the base material, and then bringing said polymer in molten condition into contact with said base wet with said liquid, said liquid containing a polymerizable monomer and being an anaerobic curing composition whose polymerization is inhibited by contact with air.

2. Process as set forth in claim 1 in which said monomer is an acrylate polyester of a polyhydric alcohol mixed with a hydroperoxide.

3. Process as set forth in claim 2 in which said monomer is tetraethylene glycol dimethacrylate, said anaerobic curing composition being stable for at least one month in air at 25 C.

4. Process as in claim 1, in which the polymer in molten condition is present as a molten bath with which said liquid-wet base is brought into said contact so as to cover said liquid with said molten polymer.

5. Process as in claim 4 and comprising continuously passing an aluminum foil from a supply thereof to said bath where said foil is embedded continuously in a layer of said polymer, and as said foil passes continuously from said supply to said bath continuously depositing on the moving uncoated foil a thin layer of said liquid.

References Cited UNITED STATES PATENTS 3,096,210 7/1963 Boonstra ll7218 X 3,140,196 7/1964 Lacy et a1. l17--75 3,401,058 9/1968 Lockie et a1. l171l5 X 2,628,178 2/1953 Burnett et a1 161-214 X 3,008,848 11/1961 Annonio 117-72 3,015,576 1/1962 Hendrixson et a1. 11749 3,218,305 ll/1965 Krieble 156-332 X OTHER REFERENCES Condensed Chemical Dictionary, 6th ed. Reinhold Publ. Corp., N.Y., 1961, pp. 464-467, 841 and 842.

ALFRED L. LEAVITT, Primary Examiner THOMAS E. BOKAN, Assistant Examiner US. Cl. X.R. 

